Depending on the application, more or less online help can be extremely useful. Some forms are better than others. Some are easier to produce, or maintain.
Often, there's a requirement for there to be a user guide, which then drives the main documentation effort. Then online Help can wind up as a re-purposed or derived form of a book-like guide -- even if the guide is never printed but only exists as PDF.
These efforts can be OK or lousy. Simply slapping a PDF up on screen is not great. You have to put some work into (re-)organization, bookmarking, hyperlinking, searchability of the user's guide to make it useful in the program.
You have to choose your delivery format based on audience, attention span, need for printed materials. Internal business applications call for training classes, which can also drive demand for a book or other training deliverable.
If your application can get by without explaining anything or showing any additional help for users while they're using it, hooray, the developers hit the jackpot and probably had a team of writers and tech communicators working alongside them.
There is no perfect development environment for all that, because it requires writing and language tools that code editors alone don't have. There are big publishing packages that promise multiple output formats, but its impossible to be perfect at too PDF, CHM, HTML authoring and output.
Visual Studio along with a content-management database and word processor (probably Word) would be one set of tools for dynamic HTML 5 Help systems. So Would Flare or FrameMaker. You still likely need a web editor (MS Expressions Web, Dreamweaver, etc.) for times when you have to work directly in the HTML. You need Photoshop or other image editor, and a versatile capture tool.
Most importantly, if you want excellent online help, you need experienced technical writers, who are really interactive documentation developers and communication specialists and much as they are "writers."